This invention relates to foams made by polymerizing emulsions containing polyelectrolytes. The emulsions comprise a continuous oil phase and a co- or discontinuous aqueous phase. The resulting foams are useful as a separations medium.
Porous polymeric materials have been produced by photo- or thermal polymerization of water-in-oil emulsions, having a relatively high ratio of water to oil phases. These emulsions, known as high internal phase emulsions (HIPEs) when the water phase is 74% or more of the total by volume, comprise a polymerizable oil continuous phase and a crosslinking agent, and a co- or discontinuous aqueous phase. To achieve the most uniform morphology, such emulsions are prepared by controlled addition of the aqueous phase to the oil phase under shear conditions in the presence of the emulsifier. See for example, U.S. Pat. Nos. 4,522,953 (Barby et al.), 6,462,100 (Thunhorst et al.), 6,353,037 (Thunhorst et al.) and WO 01121693.
The resulting polymerized emulsions have a foam structure containing cavities or cells interconnected by pores in the cavity walls. By choosing the appropriate component and process conditions, HIPE polymers with void volumes of 74% to greater than 95% can be achieved. These materials have a high capacity for absorbing and retaining fluids. Modifications of HIPE polymers have been described: U.S. Pat. No. 4,536,521 (Haq) discloses that HIPE polymers may be sulfonated to produce materials that have a high capacity for absorption of ionic solutions.
The present invention features a novel method for creating foams containing polyelectrolytes from water-in-oil emulsions. The foams may be made from high internal phase emulsions (HIPEs) whereby the emulsion is polymerized and crosslinked by exposure to actinic radiation, by heating, or a combination thereof.
One aspect of the present invention provides a process for making a crosslinked polymeric foam comprising: a) mixing an oil phase comprising at least one polymerizable monomer and at least one initiator, with an aqueous phase containing at least one polyelectrolyte (for example poly(sodium-4-styrenesulfonate)), to form an emulsion wherein the aqueous fluid forms a discontinuous or co-continuous phase with the continuous oil phase; b) optionally shaping the emulsion; and c) exposing the emulsion to actinic radiation or thermal energy to form a crosslinked polymeric foam containing the polyelectrolyte and residual aqueous phase. If desired, the emulsion may further comprise porous or nonporous organic or inorganic particles, including metal oxide particles, including surface-functionalized metal oxide particles.
In another aspect, the present invention provides a process for making a crosslinked polymeric foam comprising: a) mixing an oil phase comprising at least one polymerizable monomer and at least one initiator, with an aqueous phase containing at least one polymerizable monomer, having ionic or ionizable functional groups, to form an emulsion wherein the aqueous fluid forms a discontinuous or co-continuous phase with the continuous oil phase; b) optionally shaping the emulsion; and c) exposing the emulsion to actinic radiation or thermal energy to form a crosslinked polymeric foam containing the polyelectrolyte and residual aqueous phase.
In another aspect, the invention provides an open-coiled foam having polyelectrolytes dispersed within the cellular structure of the foam. The polyelectrolyte may form discrete domains within the cellular structure (i.e. may be an amorphous particle within the foam cells), or may coat the polymeric matrix of the foam (i.e. coat the walls of the foam cells). The foam may be used as a separations medium for the removal of various analytes from solution.
As used in this invention:
xe2x80x9cHIPExe2x80x9d or xe2x80x9chigh internal phase emulsionxe2x80x9d means an emulsion comprising a continuous oil phase, typically an oil phase, and a discontinuous or co-continuous phase immiscible with the oil phase, typically a water phase, wherein the aqueous phase comprises at least 74 volume percent of the emulsion;
xe2x80x9cwater-in-oil emulsionxe2x80x9d means an emulsion containing a continuous oil phase and a discontinuous water phase; the oil and water phases may be co- continuous in some cases;
xe2x80x9coil phasexe2x80x9d means the continuous phase which contains the monomer or organic reactive species that are sensitive to reactive propagating species (e.g., those having free radical or cationic centers) and can be polymerized or crosslinked;
xe2x80x9cstablexe2x80x9d means the composition and microstructure of the emulsion are not substantially not changing over the period required to polymerize the emulsion;
xe2x80x9cfunctional groupxe2x80x9d means a chemical entity capable of undergoing a non-polymerization reaction, such as a condensation reaction;
xe2x80x9cfunctionalized metal oxide particlexe2x80x9d means a particle prepared from colloidal materials from the group of silica, zinc oxide, titania, alumina, zirconia, vanadia, chromia, iron oxide, antimony oxide, tin oxide, other colloidal metal oxides, and mixtures thereof, functionalized such that (a) the particles disperse in the oil and/or aqueous phase and (b) chemical entities attached to the particle are capable of polymerization; these particles can comprise essentially a single oxide such as silica or can comprise a core of an oxide of one type (or a core of a material) on which is deposited the oxide of another type, an aggregate, or an agglomerate of two or more oxides;
xe2x80x9cinorganic particlexe2x80x9d means a particle that is not comprised significantly of carbon and preferably has a longest dimension of 10 microns or less and most preferably has a longest dimension of 2 microns or less
xe2x80x9corganic particlexe2x80x9d means a particle that is comprised significantly of carbon and preferably has a longest dimension of 10 microns or less and most preferably has a longest dimension of 2 microns or less
xe2x80x9cpolyelectrolytexe2x80x9d means an oligomer, polymer, or copolymer containing ionic substituents wherein an aqueous solution of the oligomer or (co)polymer will conduct an electric current;
xe2x80x9creactive surfactantxe2x80x9d means a surfactant (i.e., emulsifier) having sufficient reactivity to undergo polymerization reactions such that it becomes part of a polymer backbone;
xe2x80x9copen cellxe2x80x9d means a foam wherein the majority of adjoining cells are in open communication with each other; an open cell foam includes foams made from co-continuous emulsions in which the cell structure is not clearly defined, but there are interconnected channels creating at least one open pathway through the foam;
xe2x80x9cwindowxe2x80x9d means an intercellular opening;
xe2x80x9cshapingxe2x80x9d means forming into a shape and includes pouring, coating, and dispensing;
xe2x80x9cpolymerizexe2x80x9d or xe2x80x9ccurexe2x80x9d are used interchangeably in this application and indicate a chemical reaction in which monomers, oligomers, polymers, functionalized metal oxide particles, or other reactive species combine, including by crosslinking, to form a chain or network;
xe2x80x9ccrosslinkingxe2x80x9d means the formation of chemical links between polymer chains;
xe2x80x9ccrosslinking agentxe2x80x9d means a material that adds to a polymer chain a site capable of forming a link to another polymer chain;
xe2x80x9ccationically curable monomerxe2x80x9d means a monomer capable of undergoing polymerization in which cationic species propagate the polymerization reaction and includes monomers containing, e.g., epoxide or vinyl ether moieties;
xe2x80x9cethylenically unsaturatedxe2x80x9d means a monomer having a carbonxe2x80x94carbon double bond in its molecular structure;
xe2x80x9cactinic radiationxe2x80x9d means photochemically active radiation including near infrared radiation, visible light, and ultraviolet light and actinic radiation;
xe2x80x9cvoidxe2x80x9d means any open space, in a foam, such as holes, cells, and interstices.